The present invention relates to gas shielded tungsten-arc welding torches commonly referred to as GTAW or TIG torches, and more particularly to an improved gas lens assembly for use on such torches. In the GTAW or TIG welding process, a welding torch is used to direct electrical current in a protective inert shielding gas (usually argon) to the weld puddle area. The flow and shielding provided by the gas is critical to the quality of the weld deposit. The gas flow must be laminar as a turbulent gas flow can cause air containing oxygen and oxides to come into contact with the weld puddle and create significant weld quality problems. Over the years, various configurations of what are called gas lenses have been developed to provide a laminar flow of shielding gas to the weld puddle. Examples of such gas lens assemblies are found in U.S. Pat. Nos. 3,180,967, 4,788,401, 5,393,949, 5,556,550 and 5,772,102.
After almost forty years, the original concepts disclosed in U.S. Pat. No. 3,180,967 are still used extensively in gas lens assemblies. The gas lens system disclosed therein and others currently in use generally comprise a series of axially aligned fine mesh wire filter screens secured within the torch nozzle about the electrode between downstream end portions of the gas lens body and the surrounding gas lens sleeve. The filter screens are of a flat annular configuration, are spaced apart by inner and outer metal rings to form a series of chambers between the screens and are held in place between the gas lens body and sleeve by retaining rings or by rolling the extended edge of the surrounding sleeve about the rings and screens. While these lens systems generally provide the desired laminar gas flow, they are costly to manufacture and assemble as the component parts require precision machinery and must be individually installed.
In addition to the high cost of production, the outer screens in these gas lens assemblies are highly susceptible to damage caused by metal spatter from the molten weld puddle and from exposure to excessive heat. When molten metal spatter comes in contact with the outer gas lens screen or sintered metal disc (sometimes used in lieu of an outer screen), the spatter will adhere to or melt the screen or disc causing disruption of the laminar glass flow and rendering the gas assembly useless. Extremely high temperatures are generated by the electric arc and molten weld puddle and by stray high frequency electrical current arcing across the screen area. Excessive heat will also melt or warp the outer filter screen or sintered disc. Such damage is critical as these gas lens assemblies generally do not allow for removal of the screens or discs from the main gas lens assembly body, thus necessitating replacement of the entire assembly when the outer screen or disc becomes damaged. While U.S. Pat. No. 5,772,102 does disclose a gas control device in which the outer end of the gas lens assembly containing the mesh screens is removable, that device does not allow for individual screen replacement. It only allows for replacement of all the filter screens as a single unit. Thus, while such replacement is less expensive than replacement of the entire gas lens assembly, it is still costly as the screen unit has several parts, requiring precision machining and costly assembly time. Thus, the problems of costly construction and part replacement continues. The gas lens assembly of the present invention obviates these problems.
Briefly, the present invention is directed to an improved gas lens assembly for gas shielded arc welding torches which provides directional control and laminar flow of the shielding gas, is of an economical construction and allows for rapid replacement of the outer screens in the event of damage caused by metal spatter or excessive heat exposure. In the preferred embodiment of the present invention the lens assembly includes a conventional gas lens body and surrounding sleeve and a plurality of annular wave-shaped mesh spacer discs disposed between and axially aligned with a plurality of annular fine mesh flat inner filter screens so as to form a sandwich configuration wherein the fine mesh filter screens are held in a predetermined axially spaced relationship by the elevational component of the wave-shaped spacer discs. A plurality of flat annular outer filter screens having a coarser mesh than the sandwiched inner screens are stacked outwardly adjacent and in axial alignment with the sandwich configuration of inner screens and wave-shaped spacer discs. The inner screens, wave-shaped spacer discs and outer screens are all held in place by a single retaining ring. Each of the outer screens defines a pull-out tab projecting outwardly therefrom enabling the torch operator to peel off the outermost screen from the stack of outer screens to expose a fresh outer screen upon the outermost screen being damaged by heat or metal spatter. Alternatively, a notch can be provided in the outer end portion of gas lens sleeve surrounding the outer screens to provide access to perimeter portions of the stacked outer screens to enable the torch operator to peel off the damaged outmost screen.
In a first alternate embodiment of the present invention, a plurality of annular spacer rings are employed in lieu of the annular wave-shaped mesh spacer discs of the prior embodiment to maintain the fine mesh inner filter screens in the desired axially spaced relationship. The axial spacing between each pair of inner filter screens is defined by the thickness of the spacer ring disposed therebetween. The plurality of stacked individually removable outer filter screens having the coarser mesh are disposed outwardly adjacent the sandwiched inner screens as in the prior embodiment. In a second alternative embodiment of the present invention, the sandwiched configuration of fine mesh inner flat screens is replaced with a layer of porous filter media made of metal, ceramics or fitted glass. Again, the plurality of stacked individually removable outer filter screens having the coarser mesh are employed as described in the prior embodiments.
It is the principal object of the present invention to provide an improved gas lens assembly for gas shielded arc welding torches.
It is another object of the present invention to provide such a lens assembly which is of simple construction and economical to manufacture.
It is yet another object of the present invention to provide an efficient gas lens assembly which is compatible with most industry standard gas shielded arc welding torch models and uses traditional ceramic gas nozzles to reduce the cost of operation.
It is a still further object and advantage of the present invention to provide an improved gas lens assembly for gas shielded arc welding torches of the type using a plurality of spaced filter screens which allows for the quick and simple removal of a damaged screen at the work station without having to replace the entire gas lens assembly.
It is yet another object of the present invention to provide a gas lens assembly for gas shielded arc welding torches of the type utilizing a plurality of spaced filter screens which allows for the individual outer screens to be easily and quickly removed when damaged exposing a fresh outer screen to increase the life of the lens assembly and reduce the cost of operation.
It is a still further object of the present invention to provide an improved gas lens assembly construction for gas shielded arc welding torches which is adaptable for use with such torches of varying size and construction.
These and other objects and advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.